This invention relates to motion translation mechanisms.
More particularly, the invention concerns improvements in motion translation mechanisms of the type for converting rotary movement to reciprocal movement and for converting reciprocal movement to rotary movement.
In a further aspect, the invention concerns an improved motion translation mechanism which provides the mechanical drive assembly for a positive displacement machine.
In a still further aspect, the invention concerns a positive displacement machine having a rotatively reciprocating piston which is mechanically linked to a nutating journal of a rotating shaft.
In a yet further aspect, the invention concerns a compressor or the like in which the piston has no rubbing contact with its enclosing member.
In a yet still further aspect, the invention concerns a compressor which may easily and efficiently pump fluids or compress fluids which are free from the contamination of lubricants and provides for unidirectional flow of fluids and advantageous valving.
Motion translation mechanisms for converting rotary movement to reciprocal movement are generally well known. Earlier mechanisms of this type employed a mechanical linkage analogous to the conventional internal combustion engine, as described in United Kingdom patent No. 511,954. Herein, one end of a connecting rod is journaled on the offset bearing surface of a crankshaft which rotates about a first axis. The other end of the connecting rod imparts reciprocating motion to an element which oscillates about a second axis parallel to the first axis. While this type of mechanical drive assembly, based upon familiar components was relatively simple, it was exceedingly cumbersome and bulky and dictated that the rotating shaft and oscillating shaft had parallel axes.
Subsequently, a more sophisticated, but substantially compact, mechanical arrangement was developed for motion conversion. This type of motion conversion mechanism, as exemplified by U.S. Pat. No. 2,505,978, includes a rotating shaft having a nutating annular bearing surface integral with one end thereof. An annular bearing is retained upon the bearing surface by a cap member which is secured to the end of the annular bearing surface. A yoke disposed about the annular bearing is supported by trunnion pins which are journaled for rotatively reciprocating motion about an axis which is perpendicular to the axis of the rotating shaft. Pins, which are perpendicular to the trunnion pins, interconnect the annular bearing and the yoke and provide for relative movement therebetween.
The latter type of motion conversion mechanism was adapted to provide the mechanical drive assembly for a vane-type compressor unit as disclosed in U.S. Pat. No. 2,413,636. Each trunnion pin is extended to actuate a pair of radially opposed double-acting vane-type pistons contained within a partitioned cylindrical housing affixed to either side of the motion conversion mechanism housing. In this arrangement, four working chambers, each housing a double-acting piston and having two radially disposed intake valves and two radially disposed exhaust valves, are provided.
The foregoing configuration of rotatively reciprocating vane-type compressor never attained commercial significance. Having the piston chambers arranged in opposed relationship and having radial valving requiring substantial manifold structures to interconnect the numerous intake ports and exhaust ports, the unit is excessively bulky in relation to the volumetric capacity. The radial valving further requires a recess in the chamber wall which reduces the piston-swept area within the chamber, thus decreasing the potential compression ratio.
Extensive research, development and testing conducted by Applicant has proven that the motion translation mechanism considered as a separate unit has inherent structural deficiencies which adversely affect the stability and the service life of the assembly. The rotating shaft is supported and journaled by a single bearing intermediate the ends thereof as necessitated by the fact that a cap member must be secured to the end of the nutating bearing surface to retain the annular bearing thereon and the other end of the shaft must support a pulley or other driving means. The load upon the nutating bearing surface as it drives the rotatively reciprocating yoke applies a constantly shifting lateral force upon the rotating shaft, which rapidly destroys the shaft support bearing. Research has also shown that the force applied to the nutating bearing surface is perpendicular to the axis of the rotating shaft. Since the nutating bearing surface is at an angle to the axis of the rotating shaft, the load upon the bearing surface is absorbed by the extremes thereof which accelerates wear in these areas and imparts a barrel shape to the bearing surface.
As the motion translation mechanism wears, allowing undesired movement or "play" between the various components, the longitudinal and radial alignment of the shaft which supports the piston is impaired. Without adequate support, the vane-type piston is not stabilized within the chamber, causing excessive friction between the piston and the chamber. In an attempt to maintain proper clearances between the piston and the chamber, prior compressor art teaches the placement of a bearing within the chamber head to journal the outer end of the piston shaft. The inclusion of the latter bearing did not remedy the deficiency of longitudinal stability of the shaft or the piston and further complicated the structure by necessitating additional passages to deliver lubricating oil to the bearing.
Due to the undesirable charactersitics of motion translation mechanisms and vane-type reciprocating piston compressors utilizing such mechanisms as described above, most positive displacement machines in current usage are of the conventional reciprocating piston type. In conventional compressors and the like in general use today, it is necessary that the piston be supported within side walls, causing often unfavorable bearing loads and the necessity for lubrication in the immediate area of any fluids being pumped or compressed. Problems of this nature are only enlarged by designs which make these pistons double-acting in nature. Serious limitations are present in present designs with respect to making units of the type described small, light and inexpensive.
Positive displacement compressors in prior art systems may not be efficiently made vibration-free. Furthermore, there is serious restriction as to the use of seal materials and seal designs because of the nature of the ways in which the pistons must be supported and the difficulty in keeping fixed or relatively constant clearances between the piston and chamber walls.
It would be highly advantageous, therefore, to provide a positive displacement machine for compressors and the like which provides a fixed relationship between the piston and its chamber, may be efficiently operated without the need for lubricants in working areas, and which provides for efficient flow of fluids therethrough.